"Some of my Mac apps won't open today. I know why, and I know a re-install fixes it ... but ... sigh. Mac App Store: It Just Works* (*sometimes)," tweeted Russell Ivanovic, a mobile app developer at Shifty Jelly.

"If you have a product in the Mac App Store, be advised that the MAS had a certificate expiration over the weekend. Brace for impact," warned Rich Siegel, also on Twitter. Siegel is the founder of Bare Bones Software, and the creator of BBEdit, an HTML and text editor for the Mac.

In a support document aimed at developers, Apple said that an earlier certificate expired Sunday, Feb. 14. Developers were told that they must use the newest certificate -- issued Monday, Feb. 15 -- before submitting apps to the company for approval and placement in the Mac App Store.

Most paid apps regularly check with Apple's servers to make sure that a receipt exists for the purchase before running; the receipt is signed with a certificate.

The certificate in question was used to digitally sign app installers, according to Rich Trouton, an OS X systems administrator, who published a short explanation on his personal blog Monday.

Apple's support document said that the certificate swap would not affect iOS and TVos apps, nor Safari extensions, but added a caveat about OS X apps. "Users running OS X El Capitan (v10.11 or v10.11.1) may receive a notification that your Mac app is damaged if it utilizes receipt validation to request a new receipt from Apple," the document said. "They can resolve this issue by restarting their Mac or updating to OS X El Capitan (v10.11.2) or later."

Computerworld staffers running Mavericks latest beta -- OS X 10.11.4 -- encountered dead apps early Tuesday, including Byword, a text editor; the Fantastical 2 calendar; and Clear Day, a weather app. Some apps threw out a request for the Apple ID password used to access the Mac App Store -- in some cases only a fleeting dialog box -- but other apps just would not launch.

Restarting the Mac did not help. But as Ivanovic pointed out, dragging the applications to OS X's Trash, then reinstalling them by downloading them again from the Mac App Store, did the trick.

This story, "Repeat Mac app mess forces some to reinstall purchased programs" was originally published by
Computerworld.